In a mine, in order to carry a load such as ore and stripping from a loading place to an earth dumping site, a large number of dump trucks (mine trucks) of a loading amount of 100 tons or more are operating. The route from the loading place to the earth dumping site is fixed, and the dump trucks repeatedly go back and forth through the same route. A plurality of dump trucks (e.g., dump trucks of the same rating) are traveling in a single route, with the operation time being 24 hours. In the case of a plurality of dump trucks which are thus large and operating for a long time, a transportation efficiency which is indicated by a work amount (energy amount) per unit cost (initial cost+running cost) is regarded as important. In recent years, in aiming at an improvement in terms of this value, attention is being paid to a reduction in running cost. In this connection, there has been proposed a method of reducing consumption amount of fuel used in an engine.
The pamphlet of Internal Publication No. 2006/043619 (Patent Document 1) discloses a system which, in order to achieve a reduction in fuel consumption amount in a work vehicle (dump truck), the power that the engine can output is restricted in accordance with the load of the work vehicle. According to this document, the driver first selects, as the engine output mode, a power mode or a standard mode by a mode setting switch. In accordance with the selected output mode, the engine characteristics are determined. As compared with the power mode, in the standard mode, the engine use region is restricted, and the operation is performed with a lower output power. Further, after the selection of the output mode, the height of the load state of the work vehicle is determined from the weight of the loaded substance (loading amount) and the suspension pressure. When it is determined that the load is high, the engine use region is expanded to the high output power side, and when it is determined that the load is low, there is performed a process to narrow the engine use region to the low output power side. Thus, in the case where it is determined that the load is low, the engine output power is suppressed, whereby a surplus power is limited, and the fuel consumption amount is reduced.